Refinery offgases, such as offgases from fluid catalytic cracker units and coker units, often contain olefins, such as ethylene, which can be recovered and used in various processes. These refinery offgases often contain a mixture of gases, which may include hydrogen, methane, ethane, ethylene, and propylene, among other lighter and heavier components.
Various processes have been proposed to recover ethylene from such a mixture of gases. For example, U.S. Pat. Nos. 6,705,113, 5,979,177, 5,502,971, and 3,765,435 each relate to methods for recovering olefins from gas mixtures.
Many of these processes require ultra-low temperature refrigerant (for example, at or below −70° C.) and use methane refrigeration, or refrigeration systems that require high-purity ethylene and high purity propylene refrigerant systems, or binary refrigerant systems utilizing ethylene and propylene. Unfortunately, these high-purity streams are not always readily available on-site, and alternatives to such external refrigeration systems are needed.